Octopuses on ecstasy have been shown to become unusually sociable, prompting scientists to suggest an evolutionary link with humans.
Researchers found the notoriously antisocial sea creatures wanted to be close to each other after receiving small doses of MDMA – and even tried to hug a chamber containing another octopus.
The scientists said the findings may open up opportunities for accurately studying the impact of psychiatric drug therapies in many animals distantly related to people.
An experiment used three connected water chambers: one empty, one with a plastic action figure under a cage and one with a female or male laboratory-bred octopus under a cage.
Four male and female octopuses were exposed to MDMA by putting them into a beaker containing a liquefied version of the drug, which is absorbed by the octopuses through their gills.
Gul Dolen, assistant professor of neuroscience at the Johns Hopkins University School of Medicine and the lead investigator conducting the experiments, said after being immersed in the MDMA fluid, the octopuses: "freaked out and did all these color changes."
Scientists then lowered the dose and they became more friendly towards one another.
“They mashed themselves against one wall, very slowly extended one arm, touched the [other animal], and went back to the other side,” Dölen said.
“But when they had MDMA, they had this very relaxed posture.
"They floated around, they wrapped their arms around the chamber, and they interacted with the other octopus in a much more fluid and generous way.
"They even exposed their [underside], where their mouth is, which is not something octopuses usually do.”
Then they were placed in the experimental chambers for 30 minutes.
All four tended to spend more time in the chamber where a male octopus was caged than the other two chambers.
Dolen said:" They tended to hug the cage and put their mouth parts on the cage.
"This is very similar to how humans react to MDMA; they touch each other frequently.
"The brains of octopuses are more similar to those of snails than humans, but our studies add to evidence that they can exhibit some of the same behaviours that we can.
"What our studies suggest is that certain brain chemicals, or neurotransmitters, that send signals between neurons required for these social behaviours are evolutionarily conserved."
She added: "What our studies suggest is that certain brain chemicals, or neurotransmitters, that send signals between neurons required for these social behaviours are evolutionarily conserved."
The study was published in the journal Current Biology.